Research On Microwave Photonic Rf Signal Modulation And Frequency Conversion Technique

As an important device of radar,communication,and other electronic systems,microwave signal generator plays a decisive role in target detection accuracy and communication quality.With the rapid development of electronic technology,radio frequency(RF)system is developing towards the direction of high frequency,large bandwidth,tunable and multi-function integration.However,due to the influence of electronic bottleneck,traditional modulation signal and frequency conversion technology are confronted with narrow working band,poor tunability and vulnerability to electromagnetic interference,which can hardly meet the development needs of electronic systems.Microwave photonic technology solves the problem of large bandwidth and broadband tunability which cannot be realized by traditional microwave technology.It has good broadband response performance,low transmission loss,wideband tunability,immunity to electromagnetic interference(EMI),and good compatibility with other optical systems.Aiming at overcoming the technical difficulties of signal modulation and frequency conversion technology,this dissertation studies the tunable,large bandwidth,high frequency signal modulation and frequency conversion technology to adapt to the development needs of future electronic systems.The specific contents are as follows:In Chapter 2,a reconfigurable microwave binary modulation signal generation scheme is proposed for meeting the demand of multiple modulation format signal generation on integrated RF front-ends.By properly adjusting the amplitude of the coded signal,and using a single Dual-Polarization Quadrature Phase-Shift Keying(DP-QPSK)modulator,the modulation signal format can be switched between Amplitude Shift Keying(ASK),Phase Shift Keying(PSK),and Frequency Shift Keying(FSK).Since the filter is not used in this scheme,the generated modulation signal has good tuning performance.The experimental results indicated that such a structure can generate ASK,PSK or FSK signals with good frequency tunability.In Chapter 3,in order to meet the requirements of microwave photonic radar system,the phase coded signal generation technology is studied.To detect the near and far targets simultaneously,a dual-band phase coded signal generation scheme is proposed.In this scheme,a large bandwidth phase coded signal can be generated without any frequency correlation devices like optical filters.In addition,there is no fixed multiplier between the carrier frequencies of the two phase-coded signals so that any dual-band phase coded signals can be generated according to the application requirements of the radar system.Experimental results showed that the proposed scheme can generate binary coded signals with tunable broadband.In order to meet the application requirement of a distributed radar,a frequency-doubling dual-band polyphase coded signal generation scheme is proposed,and it can suppress the dispersion-induced power fading.In this scheme,the frequency doubling and phase coded signal are combined to effectively reduce the requirement of the local oscillator(LO)signals within a radar.It can generate the polyphase coded signal,which can effectively reduce the doppler sensitivity of a radar.Besides,the single sideband modulation(SSB)mode is used to suppress the dispersion-induced power fading and to satisfy the application demand of disperse-antenna.Experimental results show that the scheme can generate binary and quaternary dual-band phase-coded signals.In Chapter 4,for obtaining the flexible modulation format of wideband vector signal in communication system,a carrier frequency doubling vector signal generation scheme based on a polarization multiplexing Mach Zehnder modulator(PDM-MZM)is proposed and implemented experimentally.In the scheme,instead of precoding in the electric domain to generate intermediate frequency vector signals,baseband I/Q signals are directly loaded on the modulator,making the generated vector signal obtain a wider bandwidth.This scheme is reconfigurable as different modulation signals of QPSK,8-PSK,16-QAM,32-QAM and other formats can be generated flexibly by changing the level value of baseband I/Q signal.The experimental results showed that a 600-MSym/s QPSK signal with 16-GHz carrier is generated where the input LO signal is 8 GHz.After 25-km SMF transmission,the error vector amplitude(EVM)is 9.16%,and the bit error rate(BER)equals 4×10^-6,which is lower than that of the hard-decision FEC threshold.The performance in terms of EVM of the generated modulation signals is good.In Chapter 5,aiming at the demand of generating millimeter wave signal in radio-over-fiber(RoF)system,this dissertation proposes a frequency quadrupling up-conversion scheme without filter by using the polarization-dependent characteristics of an intensity modulator(IM).By adjusting the polarization controller(PC)after the DP-QPSK modulator,the±2nd LO sidebands are respectively located in two orthogonal polarization directions.The frequency quadrupling up-conversion signal is generated by using the different modulation index of two orthogonal polarization directions of an IM.Besides,the scheme can suppress the dispersion-induced power fading.The experimental results showed that a 100-MHz QPSK signal with the carrier frequency of 2 GHz can be converted up to 26 GHz.After 25-km SMF transmission,the EVM of the signal is less than 7%,which indicates that this scheme can realize high-quality long-distance transmission of millimeter wave signal.